Voltage amplifier and detector circuits



June 26, 1934. J. l. CORNELL 1,964,502

VOLTAGE AMPLIFIER AND DETECTOR CIRCUIT FiledA March 11, 1929 Inventor: James I. Cornel I K His Attorh e5.

Patented June 26, 1934 PATENT OFFICE VOLTAGE AMPLIFIER AND DETECTOR CIRCUITS James I. Cornell, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Applicaticn March 11, 1929, Serial No. 346,011

9 Claims.

The present invention relates to radio receiving apparatus and more particularly to apparatus of that character employing an electric discharge device as a bias detector which may be of the power type shown and described in the copending application of Wendell L. Carlson, Serial No. 276,732, filed May l0, 1928, and the application of John C. Warner, led concurrently herewith. 10 A bias detector of that type may comprise any suitable electric discharge device having a cathode, an anode and a control grid and is operated with relatively high input and output voltages. It is therefore provided with but one stage of audio or low frequency amplilication following it, this stage being a power output stage, for a loud speaker or other reproducing device for example. This arrangement differs from the conventional detector and two-stage amplifier ordinarily employed in such receivers and provides but a single stage of low frequency amplific-ation for use with other sources of input or signal voltage, such as the input from a phonograph record. pick-up device. This arrangement can- .not therefore be used directly for radio phonograph combinations and the like, due to the high plate impedance of the bias detector and the single amplifier stage following the detector.

lin connection with apparatus having a bias vdetector and single output or power amplifier stage in connection therewith, it has been necessary heretofore to disconnect the detector and substitute an additional stage of amplification preceding the single amplifier stage when amplifying phonograph or other signal voltages.

It is obviously desirable to avoid the necessity for an additional amplifier device and switching means which this arrangement involves, and to this end it is the object of this invention to provide a simple circuit and means in connection with a radio receiving apparatus whereby a suitable electric discharge device may be operated as a bias detector or as a voltage amplifier and may be changed at will from operation as the one to 45 operation as the other.

Another objectl of the invention is to provide means whereby the above mentioned change from detector to amplier and vice versa may be effected by the operation of a single means such as u a switch lever or the like or by a single switching operation.

My invention will however be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a simpliiied wiring diagram showing a fundamental electrical circuit embodying the invention, and Fig. 2 is a wiring diagram of a radio receiving apparatus embodying the circuit of Fig. 1 and arranged in accordance with my invention.

Referring to Fig. 1, 5 is an electric discharge device of the B-element hot cathode type, being adapted for alternating current operation by aA heater element 6, associated with the cathode 7. The control grid and anode for this device are indicated respectively at 8 and 9. The device is provided with input and output circuits 10 and 11 respectively, the former being ccnnected with control grid 8, and the latter with anode 9.

The input circuit receives radio frequency signal energy or voltage through a suitable radio frequency transformer 12, the secondary of which is tuned to a selected frequency by a variable capacitcr 13.

The output from circuit 11 is taken through an output transformer 14, the primary of which is shunted by a resistor 15, and the secondary of. which is connected with any suitable apparatus (not shown) which may be connected with =leads 16.

This device may be operated as a detector ofy the power type, as shown and described in theV above mentioned copending application of Carlson, and may be provided with the improved circuit shown and described in the copending application of Warner, Serial No. 345,498, filed March 8, 1929. In the present example the device is shown and described in connection with such improved circuits. The device receives its external bias and anode voltages from a voltage divided resistor 17, the terminals 0f which are supplied with a voltage of the polarity indicated, through leads 18 and 19. A choke coil 20 in the high voltage lead is connected between the resistor and the supply.

Anode voltage is taken from this resistor through suitably spaced tap points 2l and 22, tap point 21 being of the high voltage terminal to which the anode circuit 11 is connected. A cathode return lead 23 is connected with tap point 22, and interposed between the cathode 7 and this lead is a grid bias resistor 24 shunted by a capacitor 25, the latter having a relatively low impedance to modulation frequencies. A capacitor forming a radio frequency bypass path from the anode circuit to the cathode is provided as 110 indicated at 26. Resistor 15 limits the anode current fiowing in the primary of transformer 14 to a value below saturation, and in addition improves the performance characteristic of the transformer.

For detector operation a portion of the bias whereby a greater power out-put is provided is supplied by the voltage drop caused by anode current flowing in resistor 24 and as this current is relatively low, the additional bias required for the normal operation of this device as a power detector, is supplied in the present example, by tapping supply resistor 17 at a point more negative than the cathode return lead tap 22. This grid bias tap is indicated at 27 and is connected with a grid bias lead 28 leading to one terminal 29 of a selector switch 30, the arm or moving contact of which is connected with the low potential end of the input or grid circuit 10.

The switch 30 is provided with an alternate contact point 31 between which and point 29 the switch arm is movable, and which contact point 31 is connected with a second signal channel which may be a low frequency input channel and which is represented in the present example by a low or audio frequency transformer 32, one terminal of the secondary thereof being connected with contact point 31. The remaining terminal of the secondary is connected with the cathode return lead 23, whereby when the switch 30 is thrown to contact 3l as shown, the secondary of transformer 32 is connected with the grid or input circuit 10 of device 5 and the bias return is directly connected with the cathode return lead 23. With this arrangement the secondaries of both input transformers 12 and 32 are connected in series, the latter being inserted in the circuit at its low potential end.

When switch 30 is thrown to the position shown, provision is made through an additional switch arm 30 connected with switch arm 30 through a link 33, to close with a contact 34 and connect in parallel with resistor 24 a second resistor 35.

By this arrangement the resistance value of the self-bias means provided essentially by resistor 24, is changed and the external bias provided through lead 28 and contact 27 is removed, whereby the bias voltage applied to device 5 or its con- `trol grid is changed from one predetermined value to another and its operation changed from a bias or power detector to a voltage amplifier. In other words, the above described switching arrangement provides for reducing the grid bias of device 5 to such a point that its internal or 'anode impedance is reduced sufficiently for it to operate as a voltage amplifier, the bias voltage being obtained wholly from resistance in the cathode return lead; this resistance in the present example being supplied by resistors 24 and 35 connected in parallel.

With this arrangement, modulated radio fi'e- `quency signals may be received on a circuit 36 'connected with radio frequency transformer l2,

-and low frequency signals may be received on a circuit 37 connected with low frequency transformer 32, and the one or the other of the two signal channels thus provided may be selected at will and the signals then formed delivered to the output circuit 16 as detected or amplified signals by throwing switch 30 and its auxiliary contact arm 30 from the one position to the other.

In the position shown, the secondary of transiformer 32 is connected for self-biased operation as an amplifier, the additional anode current drawn by the device during this mode of operation being taken by resistors 35 and 15, resistor l5 being adjusted so that the anode current through the primary of transformer 14 is maintained within safe limits, and resistor 35 being so adjusted that the correct bias voltage is provided for operating the device as a voltage amplifier.

Other suitable means for changing the resistance of the self-bias means may of course be provided, but the use of a contact arm 30 connected with the switch 30 to connect a shunting resistor across the bias resistor 24, has been found to be satisfactory in practice. If incoming signals are present in the radio frequency channel they will be applied to a certain extent to the device 5 but will be detected only slightly. They may be cut oii" by any suitable means such as the usual volume control means on the receiver or as shown and described hereinafter.

When the device is operating as a bias detector, the anode current is relatively low, being approximately at the cut-off value; hence, the voltage drop in resistor 24 is relatively low, but increases with the increased anode current caused by increased carrier wave voltage applied to its input circuit. However, when the device is operating as a voltage amplifier, the voltage drop in resistor 24 and its shunting resistor 35, is relatively high and constant iuiless distortion from overloading cccurs. This bias voltage causes the device to operate somewhat below its maximum voltage as a voltage amplifier as is desirable.

A reservoir condenser 38 is connected between points 21 and 22 of the Voltage resistor divider which together with choke coils 20, serves to regulate the voltage source to a steady value, particularly when supply leads 18 and 19 are connected with a rectified alternating current source of supply. It should be understood however that circuit leads 11, 23 and 28 may be connected with other suitable sources of anode and bias voltage and that the voltage divider means is shown only by way of example as a common and well known form of supply.

Referring now to Fig. 2, a practical application of the circuit arrangement of Fig. 1 to a radiophonograph combination is shown, and the same reference numerals are used in this fig. as in Fig. l, for like parts. Thus in Fig. 2, 5 is an electric discharge device which it is desired to operate as a bias or power detector and as a voltage amplifier, and though its output transformer 14 supplies signal voltage to an output electric discharge device 39 which in turn through a transformer 40 supplies the amplified signal to a loud speaker or other suitable apparatus indicated at 41. The output device is connected directly with the supply leads 18 and 19 through the anode and cathode return leads indicated at 42 and 43 respectively. A bias resistor 44 in the cathode return lead and a suitable bypass capacitor 45 provides the device with self-bias voltage. This arrangement may be taken to represent any suitable apparatus for receiving and operating in response to the signal voltage from device 5.

Radio frequency energy received through an antenna circuit 46 or other suitable means is amplified and supplied to radio frequency transformer 12 through a radio frequency amplifier comprising a suitably tuned circuit 47 and a radio frequency amplifier device 48. This radio frequency amplifier, representing any number of suitable amplifiers preceding the detector circuit in a radio receiving apparatus, utilizes tap point l contact arm 36 or switch connected in parallel with 'to self-bias voltage supply,

27 on resistor 17 and lead 28 as its anode supply lead, and its anode circuit indicated at 49, is connected with lead 28 which :forms its anode voltage supply lead, through an additional contact arm on a switch 51. Switch 51 is also provided with contact arms 30 and 30 corresponding to and for the same purpose as those in the circuit of Fig. l. rEhe additional contact arm 50 serves to break the anode circuit oi the radio frequency amplifier to cut orf the radio frequency incoming signals to the detector while the latter is operating as a voltage amplifier and receiving low frequency signals through circuit 37. in the present example circuit 37 is connected with a volume control potentiometer 52 and a phonograph pick-up of the magnetic type indicated at 53.

With bias voltage lead 28 utilized as the anode voltage supply lead for the radio frequency amplifier, the bias lead and cathode return lead indicated at 54 and 55 respectively, are connected with voltage divider resistor 17 at points 56 and 57 respectively, which are more negative than point 27 to which lead 28 is connected. Cathode return lead is grounded as indicated at 58, and is connected with the detector cathode return lead 23 through lay-pass capacitor 59.

With the above described arrangement when the switch 5l is thrown to the position shown the radio receiving apparatus is connected to receive modulated radio frequency signals from the antenna circuit 45. With the switch in this position device 5 operates as a bias detector of the high power receiving external bias through 51, and that portion of voltage divider resistor 17 which is included between points 27 and 22, together with the bias voltage obtained by the voltage drop in resistor 24. Resistor 35 is open-circuited through the contact arm 3G' andthe anode circuit 49 of the radio frequency ampliiier is closed through contact arm 50. An additional contact arm 60 on this switch is not used in connection with the apparatus oi" the present example. Contact arm 30 also serves to disconnect the phonograph or low ireduency input from device 5 when the switch 1s thrown to the position shown. i

When switch 51 is thrown in the opposite direction for phonograph operation, bias resistor 35 1s resistor 24 through contact arm 30. Through contact arm 50 the anode circuit 49 of the radio frequency amplnier 48 is opened, thereby cutting oii signal inpvut through the radio frequency channel, and the phonograph input is connected with the grid circuit of device 5 through the contact arm 3G, the external bias voltage being at the saine time removed and the bias being then obtained wholly from voltage drop resistors 241 and 35.

Thus it will be seen that a bias detector may be arranged for operation as a voltage amplifier, whereby radio receiving apparatus embodying such detectors may by simple ineans he adapted for phonograph operation without the use oi an additional voltage ampliiier device, and that the change from de ector to amplier operation may be eiected by simple means. Such means is adapted for operation from the one signal channel to the other through the single movement of a simple switching device controlling as it does in the present example, a maximum of th ee contact arms or switching circuits one of which changes the self-bias voltage or resistance, another of which changes the grid circuit from exterial bias at the same time cutting in a low frequency input device into the grid circuit, and a third contact which cuts off the radio frequency signal input. While the method of opening the anode circuit of the radio frequency amplifier is employed in the present example as a means for cutting ofi the last named input it should be understood that any other suit able arrangement adapted for switching operation may be employed for cutting off this channel when receiving signals from the low frequency channel. Likewise any other suitable arrangement adapted for simple switching means having a single operating movement may be employed for changing the self -bias voltage.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a radio signalling apparatus, the combination with an electric discharge device having an anode, a cathode and a control grid, of means for operating said device alternatively as a bias detector or as an audio voltage amplier, said means including an input circuit connected with said control grid, an output circuit connected with said anode, a common cathode return lead for said circuits, a self-bias resistor means connected between the cathode and said cathode return lead, a source of bias voltage connected with said cathode return lead, a second input circuit connected with said cathode return lead, a selector switch connected with said rst named input circuit for selectively and separately conn ecting in circuit therewith said second named input circuit and said source of bias voltage, and a contact carried by said selector switch for changing the value of said bias resistor means when said input circuit is connected with said s cond input circuit.

2. ln a radio signalling apparatus the combination with an electric discharge device having an anode, a cathode and a control grid, of means for operating said device alternatively as a bias detector or as a voltage amplifier, said means including a source of self-bias voltage for said device, a source of additional bias Voltage for said device, two separate sources of signal voltage one of which is connected with said control grid, and a switching device movable between two alternate positions, in one of which said switching device excludes the other of said input circuits and includes said sources of bias voltage in series, and which in the other of said positions includes the other of said sources of signal voltage in circuit with the first named source of signal voltage and excludes said source of additional bias voltage, and a contact carried by said switching device for changing the value of said self bias voltage when in said last named position.

3. In a radio signalling apparatus the combi nation with an electric discharge device having an anode, a cathode and a control grid, of means for applying thereto anode and grid bias voltages, said means including a self-bias resistor across for applying thereto anode and grid bias voltages, for said device, said bias voltage having a predetermined value with respect to the anode voltage, two separate sources of signal voltage one of which is connected with the control grid of said device, and switching and circuit means for simultaneously connecting the other of said sources of signal voltage with said control grid and for changing said bias voltage to another predetermined value, said bias resistor being thereby so connected that it provides the entire value of said bias voltage.

4. The combination of device having an anode, a cathode and a control grid, of means for providing anode and bias voltages therefor, whereby it operates as a bias detector, means for applying signal voltage thereto, a second means for applying signal voltages thereto, selector means for cutting oi the signal voltage supplied through either of said means, selector means for changing the bias voltage applied to said device from one predetermined value to another predetermined value, whereby said device may be operated as an audio voltage amplifier or as a bias detector, and means for operating said selector means simultaneously.

5. In a radio-phonograph combination apparatus including a radio receiver having a bias detector, and a phonograph pick-up circuit providing an additional source of signal input, a single switching means for changing said detector from radio to phonograph input, said switching means including a circuit for changing the bias voltage applied to said detector, and a second switching circuit for connecting the detector with the phonograph pick-up circuit, said switching circuits being arranged for simultaneous operation in said switching means.

6. In a radio-phonograph combination apparatus including a radio receiver having a bias detector, and a phonograph pick-up device providing a second source of signal input, a single switching means for changing said detector from radio to phonograph input, said switching means including a circuit for changing the bias voltage applied to said detector, a second switching circuit for connecting the detector with the phonograph pick-up device, and a third switching circuit for interrupting the radio frequency signals when said detector is connected with said device, said switching circuits being arranged for simultaneous operation in said switching means.

'7. In a radio receiving apparatus, the combination with an electric discharge device having an anode, a cathode and a control electrode, of means for supplying a bias voltage for said control electrode, selector switching and circuit means connected with said device for changing said bias voltage from one predetermined value to another predetermined value whereby said device operates selectively as a bias detector and as a voltage amplier, and switching means simultaneously controllable with said last named means for applying diiering signal voltages to said device.

8. In a radio receiving apparatus, the combination with an electric discharge device having an anode, a cathode and a control electrode, of means providing separate signal voltage channels in connection therewith, means for supplying a bias voltage for said control electrode, selector switching and circuit means connected with said device for changing said bias voltage from one predetermined value to another predetermined value whereby said device operates selectively as a bias detector and as a voltage ampliiier, and means for selectively disconnecting one of said signal voltage channels, said means being connected with said last named means whereby it is controlled simultaneously therewith.

9. The combination with a radio receiving apparatus having a bias detector of the power type and a power output device connected therewith, whereby detected signals are applied directly from the detector to said power output device without intermediate amplification, and means providing additional signal voltages to be amplied, of means for adapting said detector for operation as a voltage amplier to receive and amplify said additional signal voltages, said means comprising a switch and circuit means connected therewith having one switching circuit ior changing the detector bias voltage to a predetermined value to decrease the internal impedance of said detector, a second switching circuit for applying said signal voltages thereto, and a third switching circuit for cutting off signal voltages for said detector other than said additional signal voltages.

JAMES I. CORNELL.

CERTIFICATE 0F CORRECTION.

.lune 26, i934.

Patent No. 1,964,502.

JAMES I. CORNELL.

It is hereby certified that error appears in the printed specificationl of the above numbered pa-ent requiring coriect'ion as follows: Page 3, line 138, elaim 3, for "for applying thereto anof'e and grid bias voltages," read which is developed a portion of grid bias voltage; anti that the saidLetters Patent sshoult be read with this correction therein that the same may conform to the record of the case in the Patent Uffice.

Signed and sealed this 7th day of August, A. D. 1934.

Leslie Frazer (Seal) Acting Commissioner of Patems. 

